Belts or breaker structures for tires are made of cord reinforced elastomeric or rubber plies or layers formed in strips. The cords are positioned generally parallel to each other and are spaced uniformly by a distance occupied by the elastomeric or rubber material commonly referred to as the “rivet”. The rubber or elastomer is unvulcanized during its manufacture and is generally sticky or tacky and is therefore easy to deform and to adhere to itself.
The cords of belt and breaker plies are typically metallic having brass or coated steel filaments stranded to form the cord.
The manufacture of belts or breaker strips is described in US patent publication US2003/0141021A. A belt or breaker strip is made by cutting at an angle θ a continuous roll of rubber material having reinforcement cords in the longitudinal direction. The cut pieces are in the shape of a parallelogram, having a triangular leading tip and a triangular trailing tip. The separate strips are transported to a splicing table where the trailing and leading tips are butt spliced together to form a continuous strip having all the cords oriented at the cut angle θ.
In the manufacture of a belt for a tire these strips are cut and spliced to a predetermined width to form a belt layer. Each belt layer in a tire generally has a distinct belt width and each successive layer has the cords oriented oppositely relative to the adjacent layer. Typically two layers sometimes three or four layers are used. Historically belt layers were always paired, but that is not always the case in modern tires. The belt layers restrict the growth of the underlying radial carcass plies in a radial tire. Radial tires have the ply cords angled at about 90° relative to the tires center plane. The belt layers have the cords oriented at 17° to 25° typically. Bias tires employ two or more carcass cross-plies having the cords oriented oppositely in adjacent layers between 50° and 65° generally. They use breakers in place of belts and these breakers have cord angles typically 40° to 65° and are directionally oppositely oriented between adjacent layers. For the purposes of this invention the use of the invention does not depend on the type of belt or breaker layer and in some applications the invention can be used in radial carcass plies as will be shown.
A primary goal in tire construction is building a tire with great uniformity. The manufacture of these cord reinforced strips and applying the cut strips to a tire building drum must be accomplished in a fashion that is consistently uniform to insure a manufactured tire is made to the highest standards.
Modern tire building is very equipment sensitive and involves a high degree of automated assembly. Automated assembly has the advantage of being reliably consistent and fast.
One area of tire building that has been difficult to automate is the random and extremely low occurrence of a “wild wire”. A “wild wire” as used herein is a wire filament or cord located at a cut end of a belt breaker or carcass ply that is partially separated from the rubber and thus sticking out from the layer or strip.
The occurrence of wild wires is more likely in steel cords than in textile or synthetic cords. The most likely reason being the synthetic cords when embedded in the hot rubber tend to relax and have very little residual stress or memory tending to act like a spring pulling the cord away from the rubber. Metallic cords, however, can retain some residual stress or spring-like memory. Thus occasionally if the cutting knife cuts into the cord, scraping the rubber material away on one side and pulling the cord in the direction of the cut slightly, then a portion of the wire can spring away from the layer at the cut end. Similarly if a cutting knife cuts over a cord without severing the cord, then as the strips are separated the cord will remain with that strip layer that is most strongly adhering to the cord pulling the cord from the other portion resulting in a “wild wire”.
One of the advantages of a human or manual application of such a belt layer is that wild wires are readily observable and repairable. The preferred method of repair is to simply remove the wild wire and splicing the belt layer. This leaves the belt perfectly usable and has no detrimental effect on the performance or uniformity of the tire. In an automated assembly wherein the belt layers are applied by servers the equipment may not detect a wild wire. The occurrence of a wild wire in a finished tire may not cause an issue, however, if the ends of such a wire get directed towards the air impervious innerliner then the wire can penetrate the innerliner in a crown area of the tire and can cause the tire to slowly lose air over time. Naturally it is in the tire manufacturers best interest not to sell pneumatic tires that won't hold air, accordingly it is very desirable to avoid “wild wires” altogether. Modern tire building equipment particularly belt splicers and servers have been designed to minimize such occurrences. Prior art patents EPO649730B1; U.S. Pat. No. 5,720,837; U.S. Pat. No. 5,582,664; U.S. Pat. No. 4,976,807; U.S. Pat. No. 4,961,813 and U.S. Pat. No. 4,769,104 all are representative examples of equipment used to create belts or apply such belts to tire building equipment.
Nevertheless it is in those rare occurrences of a belt with a “wild wire” being made that a simple and reliable detection system would be desirable that would alert the tire builder or equipment operator that a “wild wire” is present.
Such a detection system would enable the tires to be built in a more automated and reliable way while providing an in-line inspection system that would eliminate the “wild wire” from being processed into a finished tire.